1. Field of the Invention
This invention relates to an improved method for recovering and transporting the chemical and energy value of light normally gaseous hydrocarbons. More particularly, it relates to converting a low-molecular-weight (a light hydrocarbon) portion of petroleum to methanol and transporting a mixture of petroleum and methanol in a pipeline or tank ship to a new distant location.
2. Description of the Prior Art
For transport overland, light normally gaseous hydrocarbons have typically been transported in gas pipelines. Often, however, the cost of building a pipeline cannot be justified in relation to the quantity of gas to be transported. Petroleum is usually produced as a mixture of hydrocarbons including light normally gaseous hydrocarbons. The normally liquid portion of the crude petroleum usually is transported overland in a pipeline. Because of the high pressures involved, it is not practical to transport the light hydrocarbons along with the normally liquid hydrocarbons. If a separate pipeline for transport of the normally gaseous fraction is not available or can't be economically justified, then the light hydrocarbons are flared (burned) and the chemical and energy value of the light hydrocarbons is lost.
When the source of the crude and the marketplace are separated by an ocean and a pipeline cannot be built, then the typical means of transport of the normally liquid hydrocarbons has been by tanker. Various means for the recovery and transport of light hydrocarbons for transoceanic shipment are known in the art. For example, the July 12, 1972, Chemical Engineering, p. 35, compares the cost of shipping liquefied natural gas (LNG) via insulated and refrigerated tank ships with the cost of converting natural gas to methanol with shipment of the methanol per se in conventional tankers. The LNG option involves substantial energy consumption for compression to liquefy the gases and then for re-evaporation at the receiving terminal.
Also somewhat related to the present invention are prior art processes directed to improving the pipeline transport of crude oil. For example, in U.S. Pat. No. 3,216,435 Poettman teaches that small amounts of water, detergent solutions and other liquids may be added to a viscous oil being transported in a pipeline in order to reduce the pumping cost of the viscous liquid.
Similarly, in U.S. Pat. No. 2,821,205 Chilton et al teach minor amounts of water, up to 6 percent and preferably 0.5 to 1 percent, may be added to a viscous petroleum stream being pumped so that the water forms a lubricating film between the flowing petroleum and the inner wall of the pipeline.
Other methods for lowering crude oil viscosity for pipeline transport include the addition of a miscible gas, for example, carbon dioxide, as taught in U.S. Pat. No. 3,618,624.
The problems re efficient transport of the chemical and energy value of light hydrocarbons are also common to recovery of other viscous oil resources. For example:
(1) In the retorting of shale oil, much light gas product and a viscous oil (pour point typically about 90.degree. F.) are produced; PA1 (2) Similarly in the treatment of tar sands, much light gas product and a viscous oil are produced; PA1 (3) And in the gasification of coal, much gas product and a viscous oil are produced.
In all of these alternate oil resources and for petroleum, as discussed above, there is a need for a practical method for the recovery and transport of the chemical and energy values of these light, normally gaseous hydrocarbons.